ARM: 6047/1: ARM: BCMRING: register PMU IRQ during board initialisation

This patch updates the initialisation routine for the BCMRING platform
so that it registers its PMU IRQ with the PMU framework in the Kernel.

Acked-by: Leo Chen <leochen@broadcom.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>